Extending femtosecond stimulated raman microscopy toward silent and fingerprint region of biomolecules

In this work, the design and the implementation of a femtosecond Stimulated Raman Scattering microscope, equipped with three femtosecond laser sources: a Titanium-Sapphire (Ti:Sa), an optical parametric oscillator (OPO) and a second harmonic generator (SHG) is presented. Our microscope is designed in such a manner which has the capability to cover all the regions of Raman spectra, taking advantage of two possible laser combinations. The first, Ti:Sa and OPO laser beams, which covers the C-H region or O-H region (F > 2800 cm-1 in stimulated Raman gain (SRG) modality, whereas the second, Ti:Sa and SHG laser beams, covers the C-H region and the fingerprint region (< 1800 cm-1) and the silent region (1800 - 2800 cm-1) in stimulated Raman loss (SRL) modality. In order to demonstrate the successful realization of microscope, SRL and SRG images of polystyrene beads using the two-laser combination has been successfully reported.